The present invention relates to a system for a four-wheel drive vehicle for automatically changing the transmission system of the vehicle from two-wheel drive to four-wheel drive when the vehicle is rapidly decelerated.
In a conventional four-wheel drive vehicle, a power transmission system for two-wheel driving is selectively converted to four-wheel driving system by engaging a clutch which is manually operated by a select lever.
It is desirable for the transmission system automatically change from two-wheel drive to the four-wheel drive system under particular driving conditions such as driving on a slippery, icy or snowy road, or sudden braking, in order to prevent skidding or slipping of the wheels.